Update notes about memory context scheme.
Update notes about memory context scheme.

ahachete/gpdb,xuegang/gpdb,royc1/gpdb,xinzweb/gpdb,janebeckman/gpdb,ashwinstar/gpdb,janebeckman/gpdb,CraigHarris/gpdb,zeroae/postgres-xl,adam8157/gpdb,Chibin/gpdb,ovr/postgres-xl,zaksoup/gpdb,Quikling/gpdb,tangp3/gpdb,zeroae/postgres-xl,lintzc/gpdb,kmjungersen/PostgresXL,ahachete/gpdb,yazun/postgres-xl,yuanzhao/gpdb,yuanzhao/gpdb,zaksoup/gpdb,xinzweb/gpdb,Postgres-XL/Postgres-XL,zaksoup/gpdb,postmind-net/postgres-xl,greenplum-db/gpdb,tangp3/gpdb,janebeckman/gpdb,chrishajas/gpdb,zaksoup/gpdb,50wu/gpdb,janebeckman/gpdb,snaga/postgres-xl,lisakowen/gpdb,foyzur/gpdb,Chibin/gpdb,50wu/gpdb,kaknikhil/gpdb,Quikling/gpdb,chrishajas/gpdb,randomtask1155/gpdb,ovr/postgres-xl,lintzc/gpdb,0x0FFF/gpdb,50wu/gpdb,postmind-net/postgres-xl,zaksoup/gpdb,yuanzhao/gpdb,xuegang/gpdb,tpostgres-projects/tPostgres,postmind-net/postgres-xl,0x0FFF/gpdb,kaknikhil/gpdb,Quikling/gpdb,pavanvd/postgres-xl,tangp3/gpdb,adam8157/gpdb,cjcjameson/gpdb,royc1/gpdb,lintzc/gpdb,randomtask1155/gpdb,CraigHarris/gpdb,rvs/gpdb,CraigHarris/gpdb,randomtask1155/gpdb,rvs/gpdb,tangp3/gpdb,ashwinstar/gpdb,rubikloud/gpdb,xuegang/gpdb,ashwinstar/gpdb,cjcjameson/gpdb,0x0FFF/gpdb,oberstet/postgres-xl,yuanzhao/gpdb,rubikloud/gpdb,ovr/postgres-xl,Quikling/gpdb,Quikling/gpdb,cjcjameson/gpdb,royc1/gpdb,Chibin/gpdb,atris/gpdb,kaknikhil/gpdb,lpetrov-pivotal/gpdb,kaknikhil/gpdb,ashwinstar/gpdb,chrishajas/gpdb,janebeckman/gpdb,arcivanov/postgres-xl,rubikloud/gpdb,50wu/gpdb,janebeckman/gpdb,ashwinstar/gpdb,lpetrov-pivotal/gpdb,edespino/gpdb,janebeckman/gpdb,tangp3/gpdb,yuanzhao/gpdb,yuanzhao/gpdb,CraigHarris/gpdb,cjcjameson/gpdb,lpetrov-pivotal/gpdb,adam8157/gpdb,postmind-net/postgres-xl,atris/gpdb,edespino/gpdb,edespino/gpdb,xuegang/gpdb,0x0FFF/gpdb,ahachete/gpdb,CraigHarris/gpdb,lintzc/gpdb,tangp3/gpdb,chrishajas/gpdb,tpostgres-projects/tPostgres,royc1/gpdb,edespino/gpdb,edespino/gpdb,oberstet/postgres-xl,kmjungersen/PostgresXL,kaknikhil/gpdb,kaknikhil/gpdb,greenplum-db/gpdb,lintzc/gpdb,ashwinstar/gpdb,rvs/gpdb,foyzur/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,rubikloud/gpdb,adam8157/gpdb,arcivanov/postgres-xl,greenplum-db/gpdb,kaknikhil/gpdb,tangp3/gpdb,jmcatamney/gpdb,ahachete/gpdb,atris/gpdb,lisakowen/gpdb,foyzur/gpdb,adam8157/gpdb,techdragon/Postgres-XL,rvs/gpdb,Postgres-XL/Postgres-XL,Postgres-XL/Postgres-XL,snaga/postgres-xl,Quikling/gpdb,cjcjameson/gpdb,atris/gpdb,ovr/postgres-xl,50wu/gpdb,royc1/gpdb,edespino/gpdb,rvs/gpdb,0x0FFF/gpdb,yazun/postgres-xl,Postgres-XL/Postgres-XL,pavanvd/postgres-xl,lpetrov-pivotal/gpdb,ahachete/gpdb,greenplum-db/gpdb,lintzc/gpdb,techdragon/Postgres-XL,foyzur/gpdb,ovr/postgres-xl,zeroae/postgres-xl,snaga/postgres-xl,edespino/gpdb,arcivanov/postgres-xl,greenplum-db/gpdb,50wu/gpdb,pavanvd/postgres-xl,lintzc/gpdb,xuegang/gpdb,yuanzhao/gpdb,yazun/postgres-xl,Quikling/gpdb,ashwinstar/gpdb,lisakowen/gpdb,greenplum-db/gpdb,foyzur/gpdb,0x0FFF/gpdb,kmjungersen/PostgresXL,snaga/postgres-xl,kmjungersen/PostgresXL,atris/gpdb,rubikloud/gpdb,randomtask1155/gpdb,ahachete/gpdb,cjcjameson/gpdb,lisakowen/gpdb,lisakowen/gpdb,CraigHarris/gpdb,yazun/postgres-xl,50wu/gpdb,edespino/gpdb,yuanzhao/gpdb,foyzur/gpdb,CraigHarris/gpdb,lpetrov-pivotal/gpdb,rvs/gpdb,yazun/postgres-xl,randomtask1155/gpdb,chrishajas/gpdb,tangp3/gpdb,Chibin/gpdb,randomtask1155/gpdb,atris/gpdb,zeroae/postgres-xl,royc1/gpdb,pavanvd/postgres-xl,rvs/gpdb,postmind-net/postgres-xl,kaknikhil/gpdb,rubikloud/gpdb,lintzc/gpdb,jmcatamney/gpdb,Quikling/gpdb,foyzur/gpdb,lisakowen/gpdb,xinzweb/gpdb,xinzweb/gpdb,adam8157/gpdb,tpostgres-projects/tPostgres,chrishajas/gpdb,cjcjameson/gpdb,lpetrov-pivotal/gpdb,zaksoup/gpdb,ahachete/gpdb,randomtask1155/gpdb,50wu/gpdb,edespino/gpdb,Chibin/gpdb,rvs/gpdb,xinzweb/gpdb,Chibin/gpdb,xinzweb/gpdb,Chibin/gpdb,jmcatamney/gpdb,CraigHarris/gpdb,arcivanov/postgres-xl,janebeckman/gpdb,ahachete/gpdb,xinzweb/gpdb,Chibin/gpdb,chrishajas/gpdb,randomtask1155/gpdb,kaknikhil/gpdb,techdragon/Postgres-XL,edespino/gpdb,lpetrov-pivotal/gpdb,Chibin/gpdb,atris/gpdb,kaknikhil/gpdb,cjcjameson/gpdb,foyzur/gpdb,atris/gpdb,adam8157/gpdb,tpostgres-projects/tPostgres,yuanzhao/gpdb,zaksoup/gpdb,Postgres-XL/Postgres-XL,0x0FFF/gpdb,xinzweb/gpdb,lpetrov-pivotal/gpdb,kmjungersen/PostgresXL,arcivanov/postgres-xl,techdragon/Postgres-XL,rvs/gpdb,Chibin/gpdb,xuegang/gpdb,cjcjameson/gpdb,Quikling/gpdb,royc1/gpdb,oberstet/postgres-xl,CraigHarris/gpdb,adam8157/gpdb,zeroae/postgres-xl,lisakowen/gpdb,0x0FFF/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,zaksoup/gpdb,xuegang/gpdb,yuanzhao/gpdb,jmcatamney/gpdb,rubikloud/gpdb,lintzc/gpdb,greenplum-db/gpdb,rvs/gpdb,tpostgres-projects/tPostgres,arcivanov/postgres-xl,cjcjameson/gpdb,Quikling/gpdb,janebeckman/gpdb,oberstet/postgres-xl,greenplum-db/gpdb,rubikloud/gpdb,techdragon/Postgres-XL,xuegang/gpdb,lisakowen/gpdb,jmcatamney/gpdb,oberstet/postgres-xl,snaga/postgres-xl,xuegang/gpdb,royc1/gpdb,chrishajas/gpdb,pavanvd/postgres-xl,janebeckman/gpdb